1. Field of the Invention
The invention relates generally to energy saving devices and methods for HVAC systems and particularly to a plug and play energy saving controller (ESC or EFC) to predict and extend the fan run time of HVAC systems after the heating or cooling unit has shut off and/or to stop the compressor or heater for a short duration of time if the compressor or heater has been running continuously for fixed periods of time, while the fan is still blowing.
2. Description of the Related Art
Conventional HVAC (Heating Ventilating and Air Conditioning) systems include temperature changing components for changing the temperature and condition of air. Indoor air handlers drive air from the temperature changing component through supply ducts to zones within a building. A typical HVAC consists of heating unit, air conditioning or cooling unit or heat pump unit, and the fan or blower at the air handler unit. A thermostat is used to control the conditions of the air in a conditioned space by sending control signals to the HVAC's relays or contactors to activate or deactivate one or more of the temperature changing components.
Conventional HVAC typically runs the ventilation fan for an additional 0 second to 90 seconds after the furnace or air conditional compressor has been turned off
Studies have shown that even after this 90 seconds duration, the furnace surface and the air conditioner cooling coil still has some energy left. For example, most furnace heat exchangers are still hot (above 135 to 210° F.) after the furnace fan turns off. This wasted energy is not delivered to the conditioned space when the fan stops blowing.
Studies have also shown that if the cooling unit has been running continuously for a period of time of 20 minutes to 30 minutes, the cooling coil is wet and the evaporating of the water from the wet coil can provide additional cooling energy that can be harnessed. Also, if the heating unit has been running continuously for a period of time approximately 20 to 30 minutes, the furnace is at its maximum temperature, and by shutting down the furnace for a short period of time, but letting air flowing through it, it will not only reduce the furnace temperature therefore extending its life, but also harvest some residual heat energy for the conditioned room.
Therefore there is a need for a plug and play energy saving controller that can easily be inserted between the thermostat and the air handler of an HVAC system to recover additional heating and cooling capacity and operate HVAC equipment at higher efficiency.
There are many manufacturers of thermostats where the fan output command signal goes into a floating or unknown state when the thermostat is shut off by putting the thermostat switch to system off In many cases, when the thermostat malfunctions, one of more of its outputs goes into a high impedance state or a float state or open circuit. When a thermostat is connected directly to the air handler unit, a high impedance state or a float state will not activate the HVAC relays or contactors and therefore, the HVAC system will remain off.
There are products in the market that are connected between the thermostat and the air handler unit controllers that cannot handle a floating state as inputs. A common case is the thermostat fan output signal being in unknown state when the thermostat is switched to OFF. These products would read this as ON state, and will turn the fan on and run continuously.
Therefore, there is a need to have a circuit to read any unknown or floating signals from the thermostat fan, cool or heat command signal as known 24 vac or 0 vac state. In this way, the fan, compressor or heater will always be turned off when it is not at an ON state. Further, it would be desirable to provide a low cost controller installed between the thermostat and the air handler that will work for the majority of the thermostats in the market, that it would solve the floating state of the thermostat output signal after the thermostat is turned off and keeps the HVAC in OFF state, and that could be easily installed and operated by the user.
Thermostats that are controllable via the Wi-Fi are gaining popularity as it allows the users the flexibility of remote controls. The user can remotely turn the thermostat on or off, set the scheduling and increase or decrease the temperature set points from anywhere in the world where there is Internet or mobile data connectivity.
With the advent of the Wi-Fi enabled thermostat, and its widespread use, the utility providers such as Southern California Edison, for example, are implementing demand response (DR) using these thermostats.
DR is a set of actions taken to reduce electrical loads when the utility's electric grid could be overloaded due to excessive demands by the consumer. This is done by increasing the varying electricity rates where the demand for electricity is higher than the supply. So, usually the electricity rate is highest around 11 am to 2 pm when most of the power consumption is at its peak, and lowest around midnight when power consumption is at its lowest. Even with electricity rates at its highest during the peak periods, there are times when the peak usage is still more than what the utility can supply that may cause brownouts or rolling blackout.
A quick solution would be to increase the capacity of the generating power plants, but that means high investments, more pollution, more greenhouse effects, etc. A better solution would be to conserve. Therefore, the utility providers are resorting to rebates and incentives to the consumer to allow the utility provider access to high power consuming devices such as HVAC systems, so that these devices can be turned off for a number of times per year in exchange for credits.
Automatic Demand Response (ADR) consists of fully automated signaling from the utility provider to provide automated connectivity to the consumer's power consuming equipment to have access and control this equipment.
Open ADR is a research and standards development effort for energy managements. Open ADR provides a foundation for inter-operability of information exchange to facilitate the automated demand response. Its application is to send information and signals to cause electrical power consuming devices to be turned off during periods of high demands.
Open ADR Alliance is composed of industry stakeholders that are interested in fostering the deployment of low cost and reliable demand response communication protocols and the adoption of the common Open ADR standards. In this way, various devices produced by the manufacturers in the alliance can work with each other and with the Open ADR standards and protocols.
A WI-FI enabled thermostat with Open ADR certification is currently used by the Utility provider to manage the electrical power consumed by heating ventilation and air conditioning system (HVAC). HVAC is one of the largest consumer of electrical energy. So, if the Utility provider has the ability to control hundreds of thousands of HVAC by temporarily turning the compressor off when brownout is expected in a specific grid, then blackouts can be avoided. Also the Utility would not need to add more power plants just to service the peak demands periods.
An example of the rebate program offered by the Utility provider to its consumers is to provide free Wi-Fi enabled thermostat at no cost to the facility owner provided the facility owner allows the Utility provider to shut off the HVAC system for 10 times per year for 30 minutes per occurrence. In other instances, the rebate provided could be offering credits against the utility bill. Since these thermostats have Open ADR certification, the Utility provider is able to access these registered thermostats automatically and using automated software to carry out the program.
However, there are many homeowners who may be interested in the rebate programs, but do not wish to have their existing thermostat replaced with the WI-FI enabled thermostat. Most WI-FI enabled thermostats are complicated to set up as it involved setting up the Wi-Fi and typically is not a plug and play device. Hence, learning curve to learn and use the WI-FI enabled thermostat may be too cumbersome and technical for many home owners.
Therefore, to minimize the limitations found in the prior art, there is a need for a Wi-Fi ESC/EFC device that can be connected between an existing thermostat and the air handler of an HVAC system where the automated demand response can be implemented without having the need to replace the thermostat. Further, the Wi-Fi enabled ESC/EFC circuit device with open automated demand response capability needs to allow energy efficient operation of the HVAC system during regular operations outside of a demand response occurrence, to save even more energy.
The problems and the associated solutions presented in this section could be or could have been pursued, but they are not necessarily approaches that have been previously conceived or pursued. Therefore, unless otherwise indicated, it should not be assumed that any of the approaches presented in this section qualify as prior art merely by virtue of their presence in this section of the application.